1. Field of the Invention
The present invention relates to electric pump units.
2. Description of the Related Art
An oil pressure is supplied from a hydraulic pump to an automatic transmission of an automobile. In automobiles that perform what is called “idle reduction” (idle reduction operation) in which an engine is stopped for the purpose of energy saving etc. when the automobile is stopped, an electric hydraulic pump is used in order to ensure supply of an oil pressure to a transmission even during the idle reduction.
An electric hydraulic pump for transmissions of automobiles is mounted in a limited space in a vehicle body. There is a need to make such an electric hydraulic pump compact, and also to reduce the weight and cost of such an electric hydraulic pump. In response to such a need, an electric pump unit is proposed which contains both a pump and an electric motor for driving the pump in a common housing.
For example, an electric pump unit described in Japanese Patent Application Publication No. 2012-26349 (JP 2012-26349 A) uses, as a bearing that supports a motor shaft of an electric motor, a plain bearing rather than a rolling bearing in order to reduce the size. In order to lubricate between the cylindrical plain bearing and the motor shaft, this electric pump unit has a first oil passage extending in the axial direction from a tip end of the motor shaft and a plurality of second oil passages extending from the first oil passage to an outer peripheral surface of the motor shaft. Lubricating oil that is supplied from the tip end of the motor shaft flows through the first oil passage and the second oil passages to lubricate the plain bearing.
In this electric pump unit, however, the oil passages for supplying the lubricating oil to the plain bearing are provided in the motor shaft. It is very difficult and costs a lot to form such oil passages. It is therefore desired to ensure capability for lubricating the plain bearing and to form an oil passage with a simple structure to achieve cost reduction of electric pump units.